JP2011-106377A discloses an engine comprising an injector which is configured to inject fuel into a cylinder and a spark plug which is configured to ignite air-fuel mixture in the cylinder. The injector and the spark plug are provided at an upper portion of a combustion chamber of the engine. The injector includes multiple injection ports. The injection ports include a inject port of which a central position is located closest to a central position of a discharge gap of the spark plug. In this engine, a distance between the central position of the central position of the discharge gap and that of the closest inject port is set in advance a certain distance.
The patent publication also discloses an engine control method in which a high voltage is applied to the spark plug between after a lapse of a predetermined time from the start of fuel injection from the injector and the end of the fuel injection. To put it briefly, the engine control is a control in which an injection period is overlapped with an ignition period. The fuel splay immediately after the injection proceeds in the injection direction while taking away the surrounding air. Therefore, a low pressure part is formed in the injection period (entrainment). On the other hand, a discharge spark is generated on the discharge gap in the ignition period. Then, when the engine control in which an injection period is overlapped with an ignition period is performed, the discharge spark is attracted by the low pressure part. According to such attraction operation, the ignitability of the air-fuel mixture formed around the spark plug can be improved.
In addition, the patent publication discloses an activation control of an exhaust gas cleaning catalyst at engine start as an application example of the attraction action. Although the patent publication does not refer to, the activation control of the exhaust gas cleaning catalyst is generally performed by setting the ignition period on a retard side relative to compression top dead center. Therefore, an activation control to which the attraction action is applied means an engine control in which the fuel injection period is overlapped with the ignition period which is set on the retard side relative to the compression top dead center.
The present inventor is considering another activation control of the exhaust gas cleaning catalyst based on an engine in which a tumble flow is formed. The engine under consideration comprises an injector and a spark plug. The injector of the consideration includes multiple injection ports. The spark plug of the consideration is provided on a downstream side of the injector when viewing in a tumble flow direction at an upper part of a combustion chamber of the engine under consideration. More specifically, the spark plug is provided on a downstream side relative to a fuel spray which is located closest to the spark plug among the fuel sprays injected from the multiple injection ports, and also is provided on an upper side of a contour surface of the closest fuel spray.
The engine control under consideration is an engine control in which a first fuel injection being overlapped with the ignition period on a retard side relative to compression top dead center and a second fuel injection on an advance side relative to the compression top dead center are performed. The first fuel injection forms an air-fuel mixture which swirls in the tumble flow direction. The second fuel injection produces the low pressure part described above. Therefore, when the engine control under consideration is performed, not only the discharged spark generated in the ignition period but also an initial flame generated from the discharged spark and the air-fuel mixture are attracted to the low pressure part. Here, the air-fuel mixture causing the initial flame is derived from the first fuel injection. The initial flame attracted to the low pressure part grows in contact with the fuel spray derived from the second fuel injection and then expands by involving a remaining air-fuel mixture in the combustion chamber. The remaining air-fuel mixture is derived from the first fuel injection and has not contributed to the generation of the initial flame.
The present inventor discovered following problem in thinking of the engine control under consideration. As mentioned above, in the engine premised on the engine control under consideration, the spark plug is provided on the downstream side of the injector when viewing in the tumble flow direction at the upper part of the combustion chamber. Therefore, when comparatively strong tumble flow is generated in the combustion chamber, the initial flame and the fuel sprays move strongly. Then, despite the attraction by the low pressure part, the initial flame and the fuel sprays are not able to come in contact with the fuel spray derived from the second fuel injection and thus the combustion may become unstable. Then, when such a situation occurs frequently in the combustion cycles, combustion fluctuation between cycles increase to affect performance of the engine.
The present disclosure addresses the above described problem, and an object of the present disclosure is, in the internal combustion engine equipped with an injector provided at an upper part of a combustion chamber and a spark plug provided downstream of the injector in tumble flow direction at the upper part, to stabilize combustion during an engine control in which an ignition period by the spark plug is overlapped with a fuel injection period.